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Immunoglobulin concentrations in feline colostrum
and milk, and the requirement of colostrum for
passive transfer of immunity to neonatal kittens
Melissa A Claus BA, Julie K Levy DVM, PhD, DACVIM, Kristin MacDonald MS,
Sylvia J Tucker BS, P Cynda Crawford DVM, PhD*
Department of Small Animal
Clinical Sciences, College of
Veterinary Medicine, 2015 SW
16th Avenue, University of Florida,
Gainesville, FL 32610, USA
The purpose of this study was to clarify whether cats have a colostral and milk
phase of lactation differentiated by concentrations of immunoglobulins, and
whether colostrum ingestion by newborn kittens is essential for optimal transfer
of passive immunity. Milk from specific pathogen-free queens was analyzed for
IgG and IgA concentrations from parturition through 6 weeks of lactation.
Serum IgG and IgA concentrations from birth through 8 weeks of age were
determined for colostrum-fed kittens, colostrum-deprived kittens that were fed
a milk replacer, and colostrum-deprived kittens that were fostered onto queens
in the milk phase of lactation. The total IgG and IgA concentrations in milk were
significantly higher on the day of parturition than on day 7 of lactation,
indicating cats do have a colostral phase of lactation. The predominant
immunoglobulin in both colostrum and milk was IgG. The serum IgG
concentrations in colostrum-deprived kittens fostered on queens in the milk
phase of lactation were similar to colostrum-deprived kittens fed a milk replacer,
and the concentrations were significantly lower than in colostrum-fed kittens for
the first 4 weeks of life. The serum IgA concentrations in both colostrum-
deprived groups were significantly lower than colostrum-fed kittens on day 2
after parturition, but were similar thereafter. Colostrum-deprived kittens
fostered onto queens in the milk phase of lactation had failure of passive transfer
of maternal antibodies. Protective concentrations of immunoglobulins can be
restored in kittens with failure of passive transfer of immunity by parenteral
administration of adult cat serum, but not by fostering on queens in
mid-lactation.
Date accepted: 2 January 2006 Ó2006 ESFM and AAFP. Published by Elsevier Ltd. All rights reserved.
Passive transfer of maternal antibodies to
neonates provides protection against in-
fectious diseases before development of
their own adaptive immunity (Mason et al
1930, Brambell 1966, Simpson-Morgan and
Smeaton 1972). Many mammalian neonates rely
on ingestion of antibody-rich colostrum for pas-
sive transfer of maternal antibodies (Smith and
Little 1922, Bruner et al 1948, Comline et al
1951, Olsson 1959, Harding et al 1961, Hardy
1964, Gillette and Filkins 1966, Kruze 1970). Co-
lostrum is a transient but concentrated source
of maternal immunoglobulins, particularly IgG
and IgA (Rouse and Ingram 1970, Bourne and
Curtis 1973, McGuire and Crawford 1973, Porter
1973, Heddle and Rowley 1975, Kohn et al 1989,
Le Jan 1993, Sheoran et al 2000).
Colostral immunoglobulins ingested by the
nursing newborn are transferred intact from the
intestinal lumen into the circulation by a non-
selective transport mechanism (Brambell 1966,
Jeffcott 1971, Stott et al 1979, Staley and Bush
1985). In addition to the non-selective transport,
neonatal enterocytes have specific receptors
(FcgRn) for the uptake of IgG (Kacskovics et al
2000, Ghetie and Ward 2002, Mayer et al 2002).
The capacity for intestinal absorption of
colostral immunoglobulins decreases rapidly
and generally ceases by 24 h after parturition
*Corresponding author. Tel: þ1-352-392-4700x5731. E-mail:
crawfordc@mail.vetmed.ufl.edu
Journal of Feline Medicine and Surgery (2006) 8, 184e191
doi:10.1016/j.jfms.2006.01.001
1098-612X/06/080184+08 $32.00/0 Ó2006 ESFM and AAFP. Published by Elsevier Ltd. All rights reserved.
(Hardy 1964, Brambell 1966, Gillette and Filkins
1966, Klaus et al 1969, Jeffcott 1971, Heddle and
Rowley 1975, Casal et al 1996). Concomitant
with closure of intestinal absorption, the immu-
noglobulin concentration in mammary secretions
markedly decreases as lactation switches from
the colostral to milk phase by 3 days after partu-
rition (Rouse and Ingram 1970, Curtis and
Bourne 1971, Bourne and Curtis 1973, McGuire
and Crawford 1973, Heddle and Rowley 1975,
Norcross 1982, Le Jan 1993, Sheoran et al 2000).
The serum concentration of passively acquired
immunoglobulins in neonates is ultimately de-
termined by the quantity in the colostrum, the
volume of colostrum ingested, and the time of
ingestion. Neonates that fail to acquire adequate
amounts of antibodies before cessation of intesti-
nal absorption are at significant risk of infection.
Failure of passive transfer of immunity (FPT) is
a well-documented cause of infection-related ill-
ness and death in large animal neonates (McGuire
et al 1977, Robinson et al 1993, Raidal 1996,
Donovan et al 1998), and several colostrum re-
placements and immunoglobulin supplements
are available for prevention and treatment of FPT.
Similar to other mammalian species, neonatal
kittens rely on ingestion of colostrum for passive
transfer of maternal antibodies (Harding et al
1961, Yamada et al 1991, Casal et al 1996, Pu
and Yamamoto 1998, Levy et al 2001). Extrapola-
tion from studies in large animal species would
suggest that kittens with failure of passive trans-
fer of immunity are at significant risk for infec-
tion. Kittens at risk for FPT include those that
are orphaned or rejected before nursing, kittens
from very large litters, small or weak kittens, kit-
tens from queens that fail to lactate on the day of
birth, and kittens that must be removed before
nursing to avoid neonatal isoerythrolysis. A re-
cent study (Levy et al 2001) demonstrated that
adult cat serum administered parenterally is an
effective immunoglobulin supplement for kittens
with FPT due to colostrum deprivation. Another
study (Casal et al 1996) reported that, in contrast
to other mammalian species, immunoglobulin
concentrations were similar in feline colostrum
and milk, and proposed that newborn kittens at
risk for FPT could be fostered on queens at any
stage of lactation for acquisition of adequate pas-
sive immunity.
The purpose of this study was to clarify
whether cats have similar immunoglobulin con-
centrations in colostrum and milk, or if the
concentrations in colostrum are significantly
higher as in other species. The concentrations
of IgG and IgA were measured in colostrum
and milk samples from queens from parturition
through 6 weeks of lactation. To determine
whether the stage of lactation was important to
optimal transfer of passive immunity, serum
IgG and IgA concentrations were determined
for neonatal kittens that ingested colostrum, for
kittens deprived of colostrum and fostered on
queens in early to mid-lactation, and for kittens
deprived of colostrum and fed an artificial milk
replacer.
Materials and methods
Animals
Sixty-five blood type A specific pathogen-free
queens and their 182 kittens were included in
the study. Queens were under constant observa-
tion during the final days of gestation, and all
deliveries were attended. The research protocol
was approved by the Institutional Animal Care
and Use Committee and was conducted in facil-
ities accredited by the Association for Assess-
ment and Accreditation of Laboratory Animal
Care.
Treatment groups
There were three treatment groups in the studyd
colostrum-fed kittens, colostrum-deprived kittens
fed an artificial milk replacer, and colostrum-
deprived kittens fostered onto queens in early to
mid-lactation. All kittens were removed from the
queens immediately after birth to prevent inges-
tion of colostrum, and blood samples were col-
lected for determination of baseline serum IgG
and IgA concentrations. Kittens in each litter
were randomly assigned to either the colostrum-
fed or colostrum-deprived groups. Kittens in the
colostrum-fed group (n¼125) were immediately
returned to their queens to nurse for the duration
of the study. One group of colostrum-deprived
kittens (n¼39) was fed an artificial milk replacer
(Eukanuba Milk Replacer Formula for Kittens;
Iams) for the first 48 h postpartum, and then
returned to their queens for the duration of the
study. Another group of colostrum-deprived
kittens (n¼18) was fostered onto surrogate
queens (n¼5) that were 1e3 weeks in lactation.
Nine kittens were fostered onto two surrogate
queens that were on day 7 of lactation, five kittens
were fostered onto two surrogate queens on day
14 of lactation, and four kittens were fostered
onto a queen on day 21 of lactation. The fostered
185Immunoglobulin concentrations in feline colostrum and milk
kittens nursed for 48 h on the surrogate queens,
and then were returned to their maternal queen
for the duration of the study.
Serum and milk samples
Blood samples (1 ml) were collected via jugular
venepuncture into serum separator tubes from
all queens on the day of parturition. Blood sam-
ples (0.25 ml) were collected from kittens via
jugular venepuncture into serum separator
microtubes at parturition, on days 2 and 7, then
weekly until 8 weeks after parturition. Serum
was harvested from the blood samples by centri-
fugation. Milk (approximately 250e500 ml) was
collected daily from each queen from parturition
to day 7, then at 2, 4, and 6 weeks of lactation.
The samples were collected by gentle milking
of the secretions from several mammary glands
directly into cryovials and were not further
processed. Serum and milk samples were stored
at 80(C pending immunoglobulin analyses.
Measurement of IgG
Total IgG concentrations in serum and milk
samples were determined by a commercial radial
immunodiffusion kit (Feline IgG RID kit; VMRD,
Inc) according to the manufacturer’s instruc-
tions. Standards with IgG concentrations of
32e2000 mg/dl included with the kits were ana-
lyzed with each batch of samples. The diameter
of the precipitin ring for each standard was mea-
sured to generate a semilogarithmic standard
curve of IgG concentration versus diameter.
The standards and samples were tested in dupli-
cate. Samples with IgG concentrations more than
2000 mg/dl were diluted into the range of the
standards. Samples with IgG concentrations
less than 32 mg/dl were recorded as 0 for pur-
poses of statistical analysis.
Measurement of IgA
Total IgA concentrations in serum and milk
samples were determined by a commercial
ELISA assay (Feline IgA ELISA kit; Bethyl Labo-
ratories) according to the manufacturer’s instruc-
tions. Standards with IgA concentrations of
0.001e0.1 mg/dl provided with the kits were
included on each microtiter plate containing
test samples. The IgA standards, serum sample
dilutions (1:250e1:8000), and milk sample dilu-
tions (1:250e1:2000) were tested in duplicate. A
quadratic standard curve was generated from
the absorbance values of the IgA standards using
a software program (Microplate Manager; Bio-
Rad Laboratories). The IgA concentrations in
the test samples were calculated from the stan-
dard curve by the software program.
Statistical analysis
Data were analyzed using a software program
(SigmaStat 3.0 for Windows, SPSS, Inc). Nor-
mally distributed data with equal variance
were analyzed by the Student’s t-test. Data that
were not normally distributed or had unequal
variance were analyzed by the ManneWhitney
rank sum test. The Spearman rank order correla-
tion test was used to calculate correlation coeffi-
cients (r). For all analyses, P<0.05 was
considered significant. The data are reported as
mean SD (range).
Results
Serum and milk IgG and IgA
concentrations in queens
The total IgG concentration in serum of queens
at parturition was 1502 544 mg/dl (range,
500e2800 mg/dl). The total IgG concentration
in milk at parturition from the same queens
was 6205 2385 mg/dl (range, 1860e13,600
mg/dl). The milk IgG concentration was
4.5 1.9-fold greater (P<0.001) than the serum
IgG concentration at parturition. The milk IgG
concentrations at parturition were positively cor-
related with the serum IgG concentrations in the
respective queens (r¼0.54, P<0.001).
The total IgA concentration in serum of queens
at parturition was 190 137 mg/dl (range,
17e677 mg/dl). The total IgA concentration in
milk at parturition from the same queens was
143 116 mg/dl (range, 10e577 mg/dl). The
milk IgA concentration was not significantly dif-
ferent (P¼0.05) from the serum IgA concentra-
tion. There was no correlation between the
serum and milk IgA concentrations in the respec-
tive queens (r¼0.24, P¼0.08).
The total IgG concentration in milk from the
queens decreased significantly (P<0.001) during
the first 7 days of lactation from the peak at par-
turition of 6205 2385 to 533 729 mg/dl on
day 7 (Fig 1). The IgG concentration further de-
clined to 205 128 mg/dl by day 42 (6 weeks)
of lactation. Similarly, the total IgA concentration
in milk from the queens decreased significantly
(P<0.001) during the first 7 days of lactation
186 MA Claus et al
from the peak at parturition of 143 116 to
29 23 mg/dl on day 7 (Fig 2). The milk IgA
concentration did not change (P>0.05) further
from 1 to 6 weeks of lactation.
Serum IgG and IgA concentrations in kittens
None of the kittens had detectable IgG or IgA
in the serum at parturition. For kittens that
ingested colostrum, the peak serum total IgG
concentration on day 2 after parturition was
1915 851 mg/dl (range, 350e6000 mg/dl).
This peak concentration was positively corre-
lated with the serum IgG (r¼0.44, P<0.001)
and milk IgG (r¼0.33, P<0.001) of their dams
at parturition. Similarly, the peak serum total
IgA concentration in kittens on day 2 was
32 31 mg/dl (range, 6e176 mg/dl), and this
peak concentration was positively correlated
with the serum IgA (r¼0.19, P¼0.03) and milk
IgA (r¼0.65, P<0.001) of their dams at
parturition.
Following the peak on day 2, the maternally
derived serum IgG concentrations in the colos-
trum-fed kittens steadily declined to a nadir of
329 107 mg/dl (range, 200e600 mg/dl) at 5
weeks of age, followed by an increase to 848
425 mg/dl (range, 250e2650 mg/dl) at 8 weeks
of age (Fig 3). From the peak on day 2, serum
IgA concentrations decreased to 3 2 mg/dl on
day 7, after which the concentration remained
steady at 3e5 mg/dl (range, 1e22 mg/dl) for
the first 4 weeks of age, followed by an increase
to 21 35 mg/dl (range, 5e208 mg/dl) by 8
weeks of age (Fig 4).
There was no detectable serum IgG and IgA on
day 2 in colostrum-deprived kittens fed a milk
replacer for 48 h. For colostrum-deprived kittens
fostered on surrogate queens at 1e3 weeks of
lactation, the serum IgG concentration on day 2
was 31 30 mg/dl (range, 0e84 mg/dl), and
the serum IgA concentration was 4 2 mg/dl
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
14702128
35 42
Days of lactation
IgG (mg/dL)
*
Fig 1. Mean IgG concentrations in the milk of queens from
parturition through 6 weeks of lactation. The mean for par-
turition (day 0) represents 65 queens, the means from days 1
to 6 represent 24 to 29 queens, and the means for days 7 to 42
represent 45 to 49 queens. Error bars indicate one SD of the
mean. *The mean IgG in milk at parturition (day 0) was sig-
nificantly different from mean IgG in milk on days 1e42.
0
50
100
150
200
250
140 7 21 28 35 42
Days of lactation
IgA (mg/dL)
*
Fig 2. Mean IgA concentrations in the milk of queens from
parturition through 6 weeks of lactation. The mean for par-
turition (day 0) represents 57 queens, the means from days 1
to 6 represent 24 to 28 queens, and the means for days 7 to 42
represent 36 to 41 queens. Error bars indicate one SD of the
mean. *The mean IgA in milk at parturition (day 0) was sig-
nificantly different from mean IgA in milk on days 2e42.
0
500
1000
1500
2000
2500
3000
14
07 212835424956
Days after parturition
IgG (mg/dL)
*
*
*
**
†
†
Fig 3. Mean serum IgG concentrations from parturition
through 8 weeks of age in kittens that ingested colostrum
(n¼55e125, closed circles), colostrum-deprived kittens
that ingested milk from surrogate queens in mid-lactation
(n¼18, open circles), and colostrum-deprived kittens fed
a milk replacer (n¼39, open triangles). Error bars indicate
one SD of the mean. *Colostrum-fed kittens were significantly
different from colostrum-deprived kittens. yColostrum-
deprived kittens fed milk replacer were significantly different
from colostrum-deprived kittens fostered on surrogate
queens and colostrum-fed kittens.
187Immunoglobulin concentrations in feline colostrum and milk
(range, 1e9 mg/dl). The IgG concentration in the
milk of the surrogate queens ranged from 125 to
390 mg/dl, while the IgA concentration ranged
from 10 to 80 mg/dl. There was no correlation
of foster kitten serum IgG and IgA concentra-
tions on day 2 with the IgG (r¼0.074, P¼0.8)
or IgA (r¼0.14, P¼0.6) concentrations in the
milk of their surrogate queens. The serum IgG
and IgA concentrations on day 2 for both groups
of colostrum-deprived kittens were significantly
(P<0.001) lower than for kittens that ingested
colostrum at birth.
The serum IgG concentrations in both groups
of colostrum-deprived kittens were significantly
(P<0.001) less than colostrum-fed kittens for
the first 4 weeks after parturition (Fig 3). Starting
at 2 weeks of age, the serum IgG concentrations
in the colostrum-deprived kittens fostered on
surrogate queens or fed a milk replacer steadily
increased to 8 weeks of age due to endogenous
synthesis of antibodies (Fig 3). At 7 and 8 weeks,
the serum IgG concentrations in the colostrum-
deprived kittens fed a milk replacer were signif-
icantly (P<0.001) higher than all other kittens.
In contrast to IgG, the serum IgA concentra-
tions in the colostrum-deprived kittens fostered
on surrogate queens or fed a milk replacer
were similar to the concentrations in colostrum-
fed kittens from 1 to 8 weeks of age (Fig 4).
Discussion
The results of this study demonstrate that cats,
like most other mammalian species, have both
colostral and milk phases of lactation distin-
guished by the concentrations of IgG and IgA.
Similar to horses, pigs, and dogs (Rouse and
Ingram 1970, Bourne and Curtis 1973, Heddle
and Rowley 1975, Norcross 1982, Sheoran et al
2000), the IgG concentration was nearly five
times higher in colostrum than in serum of the
queens. This is also consistent with previous
studies in cats (Gorman and Halliwell 1989, Pu
and Yamamoto 1998, Levy et al 2001, Crawford
et al 2003, MacDonald et al 2004). In contrast to
previous studies (Casal et al 1996, Levy et al
2001, Crawford et al 2003, MacDonald et al
2004), the colostral IgG concentrations in the
current study were weakly correlated with the
serum IgG concentrations of the queen. This dis-
crepancy may be explained by the analysis of
a larger number of cats in the current study.
The predominant immunoglobulin in feline
colostrum was IgG, consistent with previous
studies in cats, dogs, horses, and pigs (Rouse
and Ingram 1970, Bourne and Curtis 1973,
Heddle and Rowley 1975, Norcross 1982, Gor-
man and Halliwell 1989, Casal et al 1996, Pu
and Yamamoto 1998, Sheoran et al 2000). As in
previous reports for cats (Gorman and Halliwell
1989, Casal et al 1996, Pu and Yamamoto 1998),
the IgA concentration in the colostrum was sim-
ilar to that in serum of the queens. Therefore, cats
are different from horses, pigs, and dogs in
which IgA is more concentrated in colostrum
than in serum (Rouse and Ingram 1970, Bourne
and Curtis 1973, Heddle and Rowley 1975,
Norcross 1982, Le Jan 1993, Sheoran et al 2000).
During the first 7 days of lactation, there was
a five-fold decrease in IgG concentration in milk
and a 10-fold decrease in IgA. The milk IgG
concentration steadily decreased throughout
lactation while the IgA concentration remained
at a constant low level for 6 weeks. These findings
are similar to previous studies in cats (Pedersen
1987, Gorman and Halliwell 1989, Pu and Yama-
moto 1998) as well as horses, pigs, and dogs
(Rouse and Ingram 1970, Bourne and Curtis
1973, McGuire and Crawford 1973, Heddle and
Rowley 1975, Norcross 1982, Sheoran et al 2000).
However, the results are contradictory to those
of another study in cats (Casal et al 1996) in which
IgG and IgA concentrations in whole and de-
fatted colostrum and milk were similar. In other
studies, including the current one, the immuno-
globulins were measured in unprocessed whole
milk samples. In pigs and cows, immunoglobu-
lins in colostrum and milk are associated with
fat globules in the cream layer (Le Jan 1993), and
0
10
20
30
40
50
60
70
147
021 28 35 42 49 56
Days after parturition
IgA (mg/dL)
*
Fig 4. Mean serum IgA concentrations from parturition
through 8 weeks of age in kittens that ingested colostrum
(n¼55e125, closed circles), colostrum-deprived kittens
that ingested milk from surrogate queens in mid-lactation
(n¼18, open circles), and colostrum-deprived kittens fed
a milk replacer (n¼39, open triangles). Error bars indicate
one SD of the mean. *Colostrum-fed kittens were signifi-
cantly different from colostrum-deprived kittens on day 2.
188 MA Claus et al
the association of immunoglobulins with milk fat
is the basis of the milk ring test for Brucella species
antibodies (Patterson et al 1974, Sutra et al 1986).
Like other species, feline colostrum and milk con-
tain substantial amounts of lipids (Keen et al 1982,
Adkins et al 1997).
In the cats in this study as well as in previous
studies (Pedersen 1987, Gorman and Halliwell
1989, Pu and Yamamoto 1998), IgG was not
only the predominant immunoglobulin in colos-
trum, but also in milk. This is similar to rumi-
nants, but different from other mammals such
as dogs, horses, and pigs in which IgA is the pre-
dominant immunoglobulin in milk (Rouse and
Ingram 1970, Bourne and Curtis 1973, McGuire
and Crawford 1973, Heddle and Rowley 1975,
Le Jan 1993, Sheoran et al 2000).
Similar to previous studies in cats (Yamada
et al 1991, Casal et al 1996, Pu and Yamamoto
1998, Levy et al 2001, Crawford et al 2003,
MacDonald et al 2004), the serum IgG concentra-
tions in kittens that ingested colostrum gradually
declined from the peak on day 2 to a nadir at 4e5
weeks of age due to catabolism of maternal IgG.
The serum IgG concentrations in colostrum-
deprived kittens fed a milk replacer or fostered
onto surrogate queens in the milk phase of lacta-
tion were significantly lower for the first 4 weeks
of life compared to kittens that ingested colos-
trum. Numerous studies in large animal species
have shown that serum IgG concentration is
the best predictor of whether neonates will be
protected against infection, and that the concen-
tration should be >400 mg/dl for adequate pro-
tection (LeBlanc et al 1992, Rea et al 1996, Franz
et al 1998, Virtala et al 1999). Large animal neo-
nates with serum IgG concentrations of less
than 400 mg/dl are diagnosed with failure of
passive transfer of immunity. Although the min-
imum IgG concentration required for adequate
passive transfer of immunity in kittens is un-
known, all of the colostrum-deprived kittens
that ingested milk from surrogate queens or
were fed a milk replacer had serum IgG concen-
trations less than 400 mg/dl for the first 4 weeks
of life, and thus had FPT based on the definition
for large animal neonates.
The serum IgG concentrations steadily in-
creased in all kittens from 4 to 8 weeks of age
due to endogenous IgG synthesis. The lower
serum IgG concentrations at 7 and 8 weeks of
age in kittens that ingested milk in the first 48 h
postpartum most likely represented suppression
of endogenous IgG synthesis by passively
acquired maternal antibodies as previously
demonstrated in pigs, calves, and foals (Jeffcott
1974, LaMotte 1977, Klobasa et al 1981, 1990).
Similar to IgG, peak serum IgA concentrations
were significantly higher in kittens that ingested
colostrum compared to colostrum-deprived kit-
tens that were fed milk replacer or fostered
onto surrogate queens. In contrast to IgG, the
serum IgA concentrations in all of the kittens, re-
gardless of whether they ingested colostrum or
not, were similar by 1 week of age and increased
at a similar rate thereafter. Previous studies in
cats and dogs reported that serum IgA concen-
trations quickly plummeted from the peak fol-
lowing colostrum ingestion to a nadir at 1e2
weeks after parturition, followed by a slow but
steady increase with age due to endogenous syn-
thesis (Poffenbarger et al 1991, Yamada et al 1991,
Casal et al 1996, Pu and Yamamoto 1998). The
reported half-life of maternally derived IgA in
kittens is approximately 2 days, which is much
shorter than that reported for maternally derived
IgG of 4e12 days (Yamada et al 1991, Casal et al
1996, Crawford et al 2003, MacDonald 2004).
In conclusion, the colostrum of cats contained
IgG concentrations greater than those in serum
while the IgA concentrations were similar to se-
rum. During the first 7 days of lactation, the
IgG and IgA concentrations in milk declined
from a peak on the day of parturition to low
levels that persisted for the duration of lactation.
Therefore, cats, similar to other mammalian
species, have both colostral and milk phases of
lactation defined by different concentrations of
IgG and IgA. Unlike other non-ruminant mam-
mals, the predominant immunoglobulin in both
colostrum and milk was IgG. Similar to colos-
trum-deprived kittens fed a milk replacer, colos-
trum-deprived kittens fostered onto surrogate
queens in the milk phase of lactation had failure
of passive transfer of immunity that persisted for
4 weeks. Kittens that are not protected by pas-
sively acquired immunity are expected to be at
greatest risk of infection during the first 4 weeks
after parturition, prior to the development of
adaptive immunity. Protective concentrations of
immunoglobulins can be restored in kittens
with FPT by parenteral administration of adult
cat serum (Levy et al 2001), but not by fostering
on queens in mid-lactation.
Acknowledgements
The authors acknowledge Megan Ross and Alex
Trapp for technical assistance. This study was
funded in part by a grant from the Harold H.
189Immunoglobulin concentrations in feline colostrum and milk
Morris Trust Fund for Research in Diseases of
Small Animals and the Merck-Merial Veterinary
Scholar Program.
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